By Thursday, the City of Churches is expected to hit 46 degrees. Sydney is expected to peak in the high 30s today, with Melbourne entering its second day in a week-long heatwave.Other capital cities are enjoying warm but less extreme temperatures.

More: Australians vent their heatwave horrors

The bureau of meterology has for the first time defined a heatwave, saying they are three or more days of unusually high maximum and minimum temperatures in any area, ABC reported.

In the last 200 years, they have taken more Aussie lives than any other form of natural disaster.

BoM. Source: HeraldSun

The BoM has also started tracking heatwaves with a new mapping system.

It measures severe heatwaves and extreme heatwaves for today and the next four days.

A similar heatwave struck before the 2009 Black Saturday fires, Australia’s worst natural disaster of the modern era in terms of casualties. An estimated 374 people died during the preceding heatwave, with another 173 fatalities in the firestorm itself.

Smoke billows from the Little River fire. Source: HeraldSun

Capital city temperatures

Melbourne – top of 41C

Adelaide – top of 45C

Canberra – top of 40C

Hobart – top of 26C

Brisbane – top of 30C

Perth – top of 26C

Darwin – top of 28C

Sydney – top of 30C

The heat is on in NSW

Most of Sydney will dodge the force of the heatwave today due to sea breezes, with temperatures staying between a mild-in-comparison 29 to 31 degrees on the coast. In the west, the mercury will rise higher – with temps smashing 37 today and peaking on Friday at an expected 39 degrees.

Sydney gets hit by the heat. Source: News Limited

Maximum temperatures in greater Sydney will probably remain in the high 30s until Saturday afternoon when a southerly moves across the city, a BoM forecaster told AAP.

Extreme heat is also in store for large parts of the rest of NSW, the forecaster said, with the town of Deniliquin, in the Riverina, tipped to cop a number of 44C days this week.

The heatwave is the result of a “very slow moving, high-pressure system sitting in the Tasman sea”, according to the bureau.

“It’s been directing steady northerly streams for a number of days now, so it’s been building a lot of heat in the interior of the continent,” she said.

Victorian paramedics are struggling to cope with the influx of heat-related patients despite recalling all available staff for this week’s heatwave.

41C at Torquay

Victoria temperatures rising quickly

Melbourne swelters through a day of temperatures in the early 40s. Federation Square.

Melbournians are set to endure the second day of the longest heatwave in 100 years.

The city reached 42.8C on Tuesday and is now set to endure four days in a row of above-40 temperatures after the bureau upgraded today’s forecast to 41C.

Firefighters tackle blazes. Source: HeraldSun

It’ll be the first time the city has endured such a heatwave since 1908, when there was a five-day streak above 40C.

People still enjoy beaches along Port Phillip Bay between St Kilda and Port Melbourne at sunset. Source: News Limited

At the Australian Open in Melbourne Park, the heat was too much for one ball boy who collapsed in a heap.

As firefighters continue to mop up in Stoneville, Parkerville and Mt Helena, authorities have confirmed the toll of properties lost at 52, with more than $13 million in damage already reported by insurers.

A fire in Stoneville has led to evacuations and loss of property. A house on Narla Retreat is lost to the flames. Source: PerthNow

The fire is also being blamed for the death of one man, 62-year-old Ron Shaw, who collapsed as he stood on the roof of his Hovea home to prepare for the arrival of the flames.

The blaze, which tore through 650ha in the Shire of Mundaring on Sunday, is now contained.

The aftermath of a bushfire is pictured in Perth’s hills on January 13. Source: Getty Images

Power remains out for about 450 homes in the region, the Department of Fire and Emergency Services (DFES) said.DFES said residents in the “zone where home have been lost” would be prevented from returning to the area today because it was “hazardous due to damaged infrastructure, downed powerlines and the risk of falling tree limbs”.

“People outside this zone are allowed to start returning to their homes, however they are required to register for a permit and access will be restricted,” DFES added in a statement.

Pregnant resident Sian Musgrove, 31, doesn’t know if her family house of 50 years is still standing. Picture: Colin Murty Source: PerthNow

The agency said a watch and act alert remained in place for the eastern part of the Parkerville, Stoneville and Mount Helena. “Firefighters will continue to strengthen containment lines and ensure the area is 100 per cent blacked out throughout,” DFES said. Counselling services have been made available to the dozens of people whose homes were razed in the fire.

Fire authorities have confirmed the blaze was most likely sparked by a fallen power pole on private property.